1. Field of the Invention
The present invention relates generally to an alternator with a rotor mounted in a vehicle, and more particularly to the rotor having a plurality of claw portions of two pole cores wherein a magnet is disposed between two adjacent claw portions in each pair.
2. Description of Related Art
An alternator for a vehicle has a cylindrical stator and a rotor disposed in the center hole of the stator. In the stator, a plurality of stator coils connected with one another are wound on a stator core. The rotor has a pair of Lundell type pole cores, a field coil wound on the pole cores, and a plurality of claw portions disposed on one end of each pole core. The claw portions of the first pole core and the claw portions of the second pole core are alternately arranged along the circumferential direction of the rotor. The rotor is configured to magnetize the claw portions by the magnetic field induced in the field coil in response to the high speed rotation of the rotor and to rotate the magnetic field strengthened by the magnetized claw portions. Therefore, the stator core placed in the rotated magnetic field is magnetized, electric power is induced in the stator coils, and the alternator outputs this electric power.
Further, a magnet is disposed between two adjacent claw portions in each pair such that the magnetic field of the magnet is directed so as to reduce the leakage of the magnetic flux induced by the magnetized claw portions. These magnets heighten the electric fields induced in the rotor, so that the outputted electric power is increased by the magnets. An alternator having these magnets is, for example, disclosed in Published Japanese Patent First Publication No. 2005-80472. In this alternator, each magnet is accommodated in a holder, and each holder with magnet is inserted into a space between two claw portions adjacent to each other.
However, in this Publication, each magnet is disposed in the holder such that the magnet is exposed to an opening of the holder. Therefore, when the alternator or rotor is covered with water, the magnet is easily exposed to the water and is wet with the water. In this case, the magnet is corroded so as to degrade the magnetic characteristics of the magnet. As a result, the output electric power is sometimes lowered. Further, when the deteriorated magnet gets a shock, the magnet is sometimes broken, and broken pieces fly out from the holder and intrude between the rotor and the stator. In this case, the broken pieces sometimes stop the rotation of the rotor.
Further, the magnets held in the holders differ from one another in size by tolerance in manufacturing. Therefore, the magnet is not fixed to the holder well, so that the magnet is insecurely fixed in the holder. In this case, the magnet is easily broken, and/or the magnet rattles in the holder.